Target device interface + plugin management

[tafk7]

Consolidate the "board" and "fgpa_part" FINN config entries with a more robust target device handler in Brainsmith. Key features must include:

• Simple yaml format to define board resources, DSP architecture, etc. See FINN's part resolver and platforms.py to get started
• Extensible registration system for custom part (potentially through plugin library, but might be unnecessary complexity for a simple dict lookup)
• Multiple names/aliases for configs (to allow lookup through board name or part number/serial)
• Blueprint integration